Filed this downstream: https://bugzilla.redhat.com/show_bug.cgi?id=986074
But our nouveau maintainer seems to be dormant at present, so filing upstream.
Running Fedora 20 (pre-release), when I boot a non-debug kernel, my graphical
rendering is mostly fine (minus a few little buglets I've been living with for
years). When I boot a debug kernel, though, it's bad - not just sluggish, but
bad. It seems like refreshes simply don't always work completely: say, I open a
new tab in Firefox, but I can still see all the content from the previous tab
until I wait several seconds or switch tabs and switch back or scrub my mouse
around a bit. Any kind of window-switching operation tends to show the issue.
A Fedora debug kernel build sets the following:
@perl -pi -e 's/# CONFIG_SLUB_DEBUG_ON is not
set/CONFIG_SLUB_DEBUG_ON=y/' config-nodebug
@perl -pi -e 's/# CONFIG_LOCK_STAT is not set/CONFIG_LOCK_STAT=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_STACK_USAGE is not
set/CONFIG_DEBUG_STACK_USAGE=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_SLAB is not set/CONFIG_DEBUG_SLAB=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_MUTEXES is not
set/CONFIG_DEBUG_MUTEXES=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_WW_MUTEX_SLOWPATH is not
set/CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_RT_MUTEXES is not
set/CONFIG_DEBUG_RT_MUTEXES=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_LOCK_ALLOC is not
set/CONFIG_DEBUG_LOCK_ALLOC=y/' config-nodebug
@perl -pi -e 's/# CONFIG_PROVE_LOCKING is not
set/CONFIG_PROVE_LOCKING=y/' config-nodebug
@perl -pi -e 's/# CONFIG_PROVE_RCU is not set/CONFIG_PROVE_RCU=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_SPINLOCK is not
set/CONFIG_DEBUG_SPINLOCK=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_VM is not set/CONFIG_DEBUG_VM=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_FAULT_INJECTION is not
set/CONFIG_FAULT_INJECTION=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAILSLAB is not set/CONFIG_FAILSLAB=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_FAIL_PAGE_ALLOC is not
set/CONFIG_FAIL_PAGE_ALLOC=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAIL_IO_TIMEOUT is not
set/CONFIG_FAIL_IO_TIMEOUT=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAIL_MAKE_REQUEST is not
set/CONFIG_FAIL_MAKE_REQUEST=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAIL_MMC_REQUEST is not
set/CONFIG_FAIL_MMC_REQUEST=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAULT_INJECTION_DEBUG_FS is not
set/CONFIG_FAULT_INJECTION_DEBUG_FS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_FAULT_INJECTION_STACKTRACE_FILTER is not
set/CONFIG_FAULT_INJECTION_STACKTRACE_FILTER=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_SG is not set/CONFIG_DEBUG_SG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_WRITECOUNT is not
set/CONFIG_DEBUG_WRITECOUNT=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS is not
set/CONFIG_DEBUG_OBJECTS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS_FREE is not
set/CONFIG_DEBUG_OBJECTS_FREE=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS_TIMERS is not
set/CONFIG_DEBUG_OBJECTS_TIMERS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS_WORK is not
set/CONFIG_DEBUG_OBJECTS_WORK=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER is not
set/CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_OBJECTS_RCU_HEAD is not
set/CONFIG_DEBUG_OBJECTS_RCU_HEAD=y/' config-nodebug
@perl -pi -e 's/# CONFIG_X86_PTDUMP is not set/CONFIG_X86_PTDUMP=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_CAN_DEBUG_DEVICES is not
set/CONFIG_CAN_DEBUG_DEVICES=y/' config-nodebug
@perl -pi -e 's/# CONFIG_MODULE_FORCE_UNLOAD is not
set/CONFIG_MODULE_FORCE_UNLOAD=y/' config-nodebug
@perl -pi -e 's/# CONFIG_SYSCTL_SYSCALL_CHECK is not
set/CONFIG_SYSCTL_SYSCALL_CHECK=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_NOTIFIERS is not
set/CONFIG_DEBUG_NOTIFIERS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DMA_API_DEBUG is not
set/CONFIG_DMA_API_DEBUG=y/' config-nodebug
@perl -pi -e 's/# CONFIG_PM_TEST_SUSPEND is not
set/CONFIG_PM_TEST_SUSPEND=y/' config-generic
@perl -pi -e 's/# CONFIG_PM_ADVANCED_DEBUG is not
set/CONFIG_PM_ADVANCED_DEBUG=y/' config-generic
@perl -pi -e 's/# CONFIG_B43_DEBUG is not set/CONFIG_B43_DEBUG=y/'
config-generic
@perl -pi -e 's/# CONFIG_B43LEGACY_DEBUG is not
set/CONFIG_B43LEGACY_DEBUG=y/' config-generic
@perl -pi -e 's/# CONFIG_MMIOTRACE is not set/CONFIG_MMIOTRACE=y/'
config-nodebug
@perl -pi -e 's/CONFIG_STRIP_ASM_SYMS=y/# CONFIG_STRIP_ASM_SYMS is not
set/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_CREDENTIALS is not
set/CONFIG_DEBUG_CREDENTIALS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_FORCE_WEAK_PER_CPU is not
set/CONFIG_DEBUG_FORCE_WEAK_PER_CPU=y/' config-nodebug
@perl -pi -e 's/# CONFIG_ACPI_DEBUG is not set/CONFIG_ACPI_DEBUG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_EXT4_DEBUG is not set/CONFIG_EXT4_DEBUG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_PERF_USE_VMALLOC is not
set/CONFIG_DEBUG_PERF_USE_VMALLOC=y/' config-nodebug
@perl -pi -e 's/# CONFIG_JBD2_DEBUG is not set/CONFIG_JBD2_DEBUG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_NFSD_FAULT_INJECTION is not
set/CONFIG_NFSD_FAULT_INJECTION=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_BLK_CGROUP is not
set/CONFIG_DEBUG_BLK_CGROUP=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DRBD_FAULT_INJECTION is not
set/CONFIG_DRBD_FAULT_INJECTION=y/' config-nodebug
@perl -pi -e 's/# CONFIG_ATH_DEBUG is not set/CONFIG_ATH_DEBUG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_CARL9170_DEBUGFS is not
set/CONFIG_CARL9170_DEBUGFS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_IWLWIFI_DEVICE_TRACING is not
set/CONFIG_IWLWIFI_DEVICE_TRACING=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DMADEVICES_DEBUG is not
set/CONFIG_DMADEVICES_DEBUG=y/' config-nodebug
@perl -pi -e 's/# CONFIG_DMADEVICES_VDEBUG is not
set/CONFIG_DMADEVICES_VDEBUG=y/' config-nodebug
@perl -pi -e 's/# CONFIG_CEPH_LIB_PRETTYDEBUG is not
set/CONFIG_CEPH_LIB_PRETTYDEBUG=y/' config-nodebug
@perl -pi -e 's/# CONFIG_QUOTA_DEBUG is not set/CONFIG_QUOTA_DEBUG=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_KGDB_KDB is not set/CONFIG_KGDB_KDB=y/'
config-nodebug
@perl -pi -e 's/# CONFIG_KDB_KEYBOARD is not
set/CONFIG_KDB_KEYBOARD=y/' config-nodebug
@perl -pi -e 's/# CONFIG_CPU_NOTIFIER_ERROR_INJECT is not
set/CONFIG_CPU_NOTIFIER_ERROR_INJECT=m/' config-nodebug
@perl -pi -e 's/# CONFIG_DEBUG_PER_CPU_MAPS is not
set/CONFIG_DEBUG_PER_CPU_MAPS=y/' config-nodebug
@perl -pi -e 's/# CONFIG_USB_UAS is not set/CONFIG_USB_UAS=m/'
config-generic
So that's the difference we're looking at. This is reproducible up to
kernel-3.11.0-0.rc6.git1.2.fc20.x86_64 .